title: Tat subunit stoichiometry in Arabidopsis thaliana challenges the proposed function of TatA as the translocation pore.
abstract: The twin arginine translocation (Tat) machinery which is capable of transporting folded proteins across lipid bilayers operates in the thylakoid membrane of plant chloroplasts as well as in the cytoplasmic membrane of bacteria. It is composed of three integral membrane proteins (TatA, TatB, and TatC) which form heteromeric complexes of high molecular weight that accomplish binding and transport of substrates carrying Tat pathway-specific signal peptides. Western analyses using affinity purified antibodies showed in both, juvenile and adult tissue from Arabidopsis thaliana, an approximately equimolar ratio of the TatB and TatC components, whereas TatA was detectable only in minor amounts. Upon Blue Native-PAGE, TatB and TatC were found in four heteromeric TatB/C complexes possessing molecular weights of approximately 310, 370, 560 and 620 kDa, respectively, while TatA was detected only in a molecular weight range below 200 kDa. The implications of these findings on the currently existing models explaining the mechanism of Tat transport are discussed.
authors.affiliation: Institut für Biologie-Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, 06120 Halle/Saale, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Jakob
authors.forename: Susanne
authors.initials: S
authors.lastname: Kaiser
authors.forename: Michael
authors.initials: M
authors.lastname: Gutensohn
authors.forename: Peter
authors.initials: P
authors.lastname: Hanner
authors.forename: Ralf Bernd
authors.initials: RB
authors.lastname: Klösgen
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D021381:Protein Transport; D012995:Solubility; D013045:Species Specificity; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D021122:Protein Subunits